The pulmonary endothelium is known to alter the composition of vasoactive substances in the pulmonary circulation, thereby potentially having the ability to influence the resistance of blood vessels in the vicinity of and distal to the site of the alterations. Severe hypoxia, hyperoxia and radiation injure the endothelium and may change biochemical and metabolic functions of the endothelium. We plan to use the bovine pulmonary artery endothelial cell in culture and the isolated perfused rat lung to assess the influences of hypoxia, hyperoxia and radiation on endothelial functions that may alter vasoactivity of the pulmonary circulation. Functions to be tested will include: the active transport of the amine, serotonin; the passive or facilitated diffusion of the nucleoside, adenosine; and the conversion of the polypeptide, angiotensin 1 to angiotensin 2. Possible mechanisms for alterations of these separate functional processes of the endothelium will be examined by determining the influences of hypoxia, hyperoxia and radiation on intermediary metabolism of these substances and on cellular ATP, Na+ K+ ATPase and substrate affinity. The studies will include assessments of the effect of injury on cellular ectoenzymes (AMPase, ADPase, ATPase) and on cellular release of adenine nucleoside and nucleotides. Where appropriate, changes in transport or enzymatic activity will be temporally correlated with morphological changes observed by electron microscopy. We hope to eventually correlate our observations with the physiological function of the pulmonary vasculature that has been subjected to hypoxia, hyperoxia or radiation. The significance of the proposed studies is that they should provide better insights into possible mechanisms by which injury to the pulmonary endothelium may alter pulmonary vascular tone and vasoreactivity and may lead to new approaches for prevention or therapy of pulmonary hypertension.